Competition between natural populations of Dactylis glomerata

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Abstract
The competitive abilities of two natural populations of Dactylis glomeratafrom Norway and Portugal were studied under three controlled environments, 7 °C with an 8 h photoperiod, 20 °C with a 16 h photoperiod, and 30 °C with a 16 h photoperiod. The temperature and daylength treatments affected both the growth habits and the relative competitive abilities of the populations. At 7 °C, 8 h photoperiod the Norwegian population became prostrate and was suppressed in mixed culture compared with its performance in monoculture, and an increased specific leaf area indicated competition for light. At 30 °C, 16 h photoperiod the Norwegian population was more erect than the Portuguese, and more aggressive, with a better performance in mixed culture than in monoculture. The performance of the Portuguese population was not affected significantly either by culture or by environment. At 20 °C, 16 h photoperiod, however, the Portuguese population was suppressed, while the Norwegian population performed better in mixed than in monoculture. This yield increase of the Norwegian population was greater than the decrease of the Portuguese population, and so the mixed culture yielded significantly more than the mean of its component monocultures, whereas at 7 and 30 °C the mixed culture yielded no more than the mean of its monocultures. The physiological basis of these competitive effects is discussed.